1. Field of the Invention
The present invention relates to a variable inertial mass flywheel whose inertial mass can be varied according to fluctuations of engine speed, and more specifically to a variable inertial mass flywheel whose response characteristics to engine speed fluctuations can be improved markedly.
2. Description of the Prior Art
In general, when the inertial mass of a flywheel is determined large, the flywheel can effectively absorb fluctuations of engine torque (referred to as torque ripple, hereinafter). On the other hand, however, the engine torque response characteristics of the flywheel is degraded in particular when an engine is accelerated. To overcome the above-mentioned problems, variable inertial mass flywheels have been proposed such that the inertial mass is large when torque ripple is large (as when the engine is being idled at low speed) but small when higher engine torque response characteristics are required (as when the engine is being accelerated to high speed).
An example of the prior-art variable inertial mass flywheel is disclosed in Japanese Published Unexamined (Kokai) Utility Model Application No. 58-30053, for instance. FIG. 1 shows this prior-art variable inertial mass flywheel 1, in which a main flywheel member 2 connected to an engine crankshaft (not shown) is rotated by an engine (not shown).
A subflywheel member 4 is rotatably attached to the main flywheel member 2 via a bearing 3. When the engine is rotating at low speed (e.g. being idled), the subflywheel member 4 is coupled to the main flywheel member 2 to increase the inertial mass, that is, to effectively absorb engine torque ripple. On the other hand, when the engine is rotating at high speed (e.g. being accelerated), the subflywheel member 4 is decoupled from the main flywheel member 2 to decrease the inertial mass, that is, to improve the engine torque response characteristics. In this case, the subflywheel member 4 is coupled to or decoupled from the main flywheel member 2 by magnetizing or demagnetizing electromagnetic powder 8 with an electromagnetic coil 9 in order to change frictional force in the electromagnetic powder 8. The electromagnetic powder 8 and the coil 9 are enclosed within an elctromagnetic chamber 7 formed by the inner circumferential surface of the main flywheel member 2, the outer circumferential surface of the subflywheel member 4, the inner surface of a cover member 5, and a seal member 6. The electromagnetic coil 9 is energized by a voltage supplied from a power supply (not shown). In more detail, when engine torque ripple exceeds a reference level, the electromagnetic coil 9 is energized to increase the inertial mass of the flywheel 1.
In the above-mentioned prior-art variable inertial mass flywheel, however, since the inertial mass is varied by magnetizing or demagnetizing electromagnetic powder 8 enclosed between the main flywheel member 2 and the subflywheel member 4, there exists a problem in that charge in frictional force of the electromagnetic powder 8 caused by electromagnetic magnetization and demagnetization is not large and not stable, and therefore the response characteristics of inertial mass to engine speed fluctuations is low, so that it is impossible to stably obtain sufficient change in inertial mass of the flywheel.
In more detail, even if the electromagnetic powder 8 is magnetized, the density of the electromagnetic powder 8 only near the electromagnetic coil 9 is increased and therefore it is difficult to sufficiently increase the frictional force uniformly in the powder 8. In addition, since the two opposing areas of the inner circumferential surface of the main flywheel member 2 and the outer circumferential surface of the subflywheel member 4 are not broad, the frictional force is not sufficiently large and therefore the two flywheel members 2 and 4 are not coupled tightly, so that it is difficult to sufficiently change the inertial mass.